As shown in FIG. 1, a tire pressure gauge 10 of the prior art is composed of a head 11 via which the high pressure air in the tire is introduced into the gauge, a piston rod 11A, a base 12, and a drive member 13 capable of being pushed by the piston rod 11A to slide such that a rotary shaft 14 is actuated by teeth 13A of the drive member 13, and that a hand (not shown in the drawing) which is fastened with one end of the rotary shaft 14 is actuated to turn to indicate the air pressure of the tire. The drive member 13 is provided with an adjusting screw 15, whereas the base 12 is provided with a spring 16 which is fitted at one end 16A thereof over the adjusting screw 15 and is fastened at other end thereof with a stop plate 17 of the base 12. The stop plate 17 has a through hole 17A, whereas the base 12 has a through hole (not shown in the drawing) corresponding in location to the through hole 17A. As a result, the fastening depth of the adjusting screw 15 can be adjusted with a screwdriver which is inserted into the base 12. The tension of the spring 16 can be thus set up to determine the sliding resisting force of the drive member 13 for correcting the measuring error of the tire pressure gauge 10.
In operation, as the head 11 is disengaged with the air valve of the tire, the hand of the gauge 10 is retained at a position by the retaining force of an arresting piece 18 of the rotary shaft 14. When a button 18A located at one end of the arresting piece 18 is pressed by the user of the gauge 10, the rotary shaft 14 is released by the arresting piece 18, thereby causing the spring 16 to force the drive member 13 to return to its original position. The hand is thus caused to point at zero of the pressure scale.
Such a tire pressure gauge 10 of the prior art as described above is defective in design in that it is complicated in construction, and that it is therefore not cost-effective, and further that the adjustment of the adjusting screw 15 can not be easily done with a screwdriver in view of the fact that the user can not see the adjusting screw 15.